1. Field of the Invention
The invention relates to a method of manufacturing a flat panel display, and more particularly to a method for thinning a flat panel display and preventing a pad electrode in a pad area from oxidizing.
2. Description of the Related Art
Recently, in order to fulfill the requirements of high-speed image processes and high quality image displays, flat panel displays, such as the color liquid crystal display (LCD), are enormously popular. The LCD usually includes a lot of pixels, each pixel has a thin film transistor (TFT) to switch on/off the pixel.
Generally, the LCD has an upper and a lower substrate having a plurality of electrodes thereon, respectively. These substrates are sealed with adhesive materials, and a liquid crystal material is sealed between these two substrates. Before the liquid crystal is injected between the two substrates, spacers are sprayed between the substrates in order to hold a constant distance therebetween. Conventionally, many TFTs are formed above the lower substrate as switching devices. Each TFT has a gate electrode connected to a scanning line, a drain electrode connected with a signal line, and a source electrode connected to a pixel electrode. The upper substrate includes a color filter and a common electrode.
FIG. 1A through FIG. 1C are sectional views illustrating a conventional method of manufacturing a liquid crystal display.
As shown in FIG. 1A, a first substrate 1 having a pad area I and a display area II is provided. A pad electrode 3 is formed on the pad area I. The pad electrode 3 is made of metal, such as Cr, Ta, Mo, Ti, or Al. A plurality of TFTs are formed on the display area II. Each TFT has a gate electrode 4, a source electrode 11, and a drain electrode 12. An insulating layer 5 is formed on the gate electrode 4. A semiconductive layer 6 is formed on the insulating layer 5. The doped silicon layers 8, 9 are formed on the semiconductive layer 6. A source electrode 11 is formed on the doped silicon layer 8, and a drain electrode 12 is formed on the doped silicon layer 9. A pixel electrode 14 is formed on the source electrode 11 and the drain electrode 12. The pixel electrode 14 is usually made of Indium Tin Oxide (ITO). Finally, a passivation layer 16 is formed to cover the first substrate 1.
As shown in FIG. 1B, in the pad area I, the passivation layer 16 and the insulating layer 5 are patterned by a suitable photolithography and etching process, and thus the pad electrode 3 is exposed. The exposed pad electrode 3 is used to connect with an external circuit.
As shown in FIG. 1C, a second substrate 2 with a predetermined size is provided. Before the liquid crystal is injected between the first substrate 1 and the second substrate 2, these substrates 1, 2 are sealed by a sealing material 18 at the appropriate temperature of 150xc2x0 C. -250xc2x0 C. The sealing material 18 is spread on the periphery of the two substrates 1, 2.
The above-mentioned method for fabricating the liquid crystal display, however, has the problems described below.
(1) A heating step is needed during the sealing process. At the same time, the surface of the metal pad electrode may be oxidized to form a metal oxide. A short circuit may happen between the pad electrode and the external circuit, and the signal transmission may be poor because of the metal oxide.
(2) There is no step for thinning the substrate in the prior method. An extra step for reducing the thickness of at least one substrate is added when a thinner display is needed.
It is an object of the present invention to provide a method of manufacturing a flat display in which the thickness of at least one substrate is reduced without any excess steps.
Another object of the invention is to provide a method of manufacturing a flat display, in which a pad electrode is not easily to be oxidized.
To achieve the above objects, a method of manufacturing a flat display according to the invention is disclosed. First, providing a first substrate having a first thickness. The first substrate includes a first display area and a first pad area, a pad electrode is formed in the first pad area, and a passivation layer is formed on the pad electrode. Next, providing a second substrate having a second thickness. The second substrate includes a second display area and a second pad area, the second display area is opposite to the first display area, and the second pad area is opposite to the first pad area. The first substrate and the second substrate are assembled and sealed by a sealing material. The second pad area of the second substrate is removed by a cutting process. The passivation layer on the first pad area is then removed by an etching process in order to expose the pad electrode. The first substrate also becomes thinner in the etching process. Therefore, the thickness of the first substrate is reduced from the first thickness to the third thickness.
The thickness of both the first and second substrates can be reduced by the etching process while the passivation layer is removed. Therefore, the thickness of the second substrate is reduced from the second thickness to the fourth thickness.
The etching process can be a wet-etching process. The ratio of the etching rate Rpass of the passivation layer to the etching rate Rsubs of the first or second substrate is in a range of 10:1 to 1000:1 according to the required thickness of the passivation layer and the substrates.
A plurality of thin film transistors are formed on the first substrate, and a color filter is formed on the second substrate. The method of manufacturing the flat display further includes a step of injecting the liquid crystal material between the first and second substrates after the step (C).
One feature of the invention is that the pad electrode is exposed by removing a part of the passivation after the first and second substrates are assembled and sealed. Therefore, the pad electrode will not be oxidized during the sealing process, and a better connection is provided between the pad electrode and the external circuit.
Another feature of the invention is that the thickness of the first and second substrates can be reduced by the same etching process for removing the passivation layer. Therefore, a lighter display can be made without adding any extra step.
Another feature of the invention is that the step of removing the passivation layer within the pad area is shifted to one step of packaging the TFT liquid crystal display. Therefore, one mask for forming an opening to expose the pad electrode can be eliminated, thus the manufacturing cost can be reduced.